The present invention relates to compositions of water-repellent coatings on the surface of liquid jet nozzles and in particular a nozzle plate for an inkjet printer.
Among inkjet heads, those using a piezo-electric element have recently become more and more popular for their high energy-efficiency, etc. This kind of inkjet head typically comprises a piezo-electric element, one common ink chamber with ink supplied from outside and stored therein, a plurality of pressure chambers connected to the piezo-electric element and a nozzle plate connected to the pressure chambers so that a nozzle is connected to each pressure chamber. Each pressure chamber that is connected each corresponding ink feed path to the common ink chamber receives ink from the common ink chamber, increases an internal pressure by utilizing a deformation of the piezo-electric element, and thereby jets ink from the nozzle.
On the surface of the nozzle plate (opposite to the pressure chamber) a water-repellent coating is typically formed around the nozzle. The water-repellent coating has the following exemplary effects. First, the water-repellent coating serves to stabilize a flying direction of ink jetted from the nozzle. Without the water-repellent coating, onto the nozzle plate surface is adhered the ink spouted from the pressure chamber, the ink adhered onto the nozzle plate like this pulls the next ink jetted continuously, and thereby bends the flying direction of ink and prevents from flying straight in a desired direction. Secondly, the water-repellent coating serves to smooth a wiping process. After a printing operation is completed, the inkjet head usually undergoes a backup process that eliminates dirt from the nozzle. In the backup process, a suction pump contacts the nozzle and sucks out dirt therein, and at the same time the ink in the nozzle adheres onto the surface of the nozzle plate. Thus, the wiping process that a wiper such as rubber blade, etc. wipes ink on the nozzle surface follows. In that event, without the water-repellent coating, the ink adhered onto the nozzle plate surface after the backup process could not successfully be wiped out and would remain on the nozzle plate surface. Consequently, the subsequently flying direction of ink is bent and printing quality is adulterated with impure or diluted color if the remaining ink is different in color from the subsequently flying ink.
For the forgoing effects, it is inevitable for inkjet head to form the water-repellent coating. In addition, a conventional water-repellent coating has a fluoric polymer of high water repellency as a main ingredient.
However, the fluoric polymer is soft and less adhesive to a substrate, and thus is likely to flaw, abrasion or scratch (i.e. low wiping-resistant); therefore, its anticipated water repellency can not be continuously maintained. Accordingly, it has been desired to form a water-repellent coating that has a fluoric polymer as a main ingredient and is continuously usable about one hundred thousand times.
Conventionally, it has been suggested for example that a fluoric polymer is plated and a subsequent heating process melts the fluoric polymer adhered onto the plated surface, forms a coating and thereby improves its wiping resistance. This process, however, involves a problem that the coating, even if it is formed, is worn out shortly by a plural of frictions and its water repellency lowers. On the other hand, it has also been suggested to form a member around the liquid jet in concave shape and avoid the fluoric coating around the nozzle from scratched by a friction. The unleveling process, however, increases its person-hours and costs.
Accordingly, it is a general object of the present invention to provide a novel and useful water-repellent coating and method of forming the water-repellent coating in which the above disadvantages are eliminated.
More specifically, it is an exemplified object of the present invention to provide a water-repellent coating that has higher wiping resistance relative to a wiper and is formed by a more simplified process than was previously possible, and a method of forming such a water-repellent coating.
In order to achieve the above object, a print head according to claim 1 comprises a nozzle plate having a nozzle which jets ink, and a water-repellent coating that is formed on the nozzle plate as a substrate around the nozzle and comprises a hard body and a fluoric polymer formed by a plating process. According to the print head claimed in claim 1, water repellency of the fluoric polymer works against liquid like ink, etc. jetted from the nozzle, and the hard body enhances wiping resistance of the fluoric polymer.
A print head as set forth in claim 2 that depends upon claim 1 comprises a water-repellent coating including the hard body in a flat shape. Thus, according to the print head claimed in claim 2, the hard body is less likely to fall off than a spherical shaped one and serves to maintain wiping resistance for a long time. A print head as set forth in claim 3 that depends upon claim 1 comprises a water-repellent coating including the hard body having a major axis of 1 xcexcm or smaller in its particle diameter. According to the print head claimed in claim 3, the hard body having a big particle diameter never prevents a nozzle plate surface from being smoothly wiped. A print head as set forth in claims 4 and 5 that depends upon claim 1 comprises a water-repellent coating having the hard body including a boron nitride boron nitride single crystal. Therefore, according to the print head claimed in claims 4 and 5, the boron nitride or boron carbide single crystal intrinsically having the advantage of a flat shape requires no additional process to deform the hard body into a flat shape. A print head as set forth in claims 6 and 7 that depends upon claim 1 comprises a water-repellent coating employing an electrolytic or electroless plating process as the plating process. Accordingly, the print head claimed in claims 6 and 7 has the advantage of requiring no special plating process.
A recording device as set forth in claim 8 comprises a print head and a driving device which drives the print head wherein the print head includes a nozzle plate having a nozzle which jets ink and a water-repellent coating which is formed on the nozzle plate as a substrate around the nozzle and comprises a hard body and a fluoric polymer formed by a plating process. According to the recording device claimed in claim 8, water repellency of the fluoric polymer works against liquid like ink, etc. jetted from the nozzle, and the hard body enhances wiping resistance of the fluoric polymer.
A method of forming a water-repellent coating as set forth in claim 9 comprises the steps of forming on a nozzle plate a first resist which is open only around a nozzle of the nozzle plate, forming a first layer of a plated fluoric polymer by a first plating process via the first resist, forming a second resist, adding a hard body to a first layer by a second plating process, and removing the first and second resists. According to the method of forming a water-repellent coating claimed in this claim, the hard body is allowed to protrude from the water-repellent coating surface because the water-repellent coating is formed on the nozzle plate as a substrate. A method claimed in claim 10 that depends on claim 9 further comprises the step of heating the water-repellent coating until its water repellency becomes enough to make a contact angle of ink containing 10% of alcohol 60 degrees or larger. By the heat treatment, the fluoric polymer melts and taking in the additive hard body.
Other objects and further features of the present invention will become readily apparent from the following description and accompanying drawings.